Feed the birds

Songbird study offers new insights into how malnutrition impairs development and cognition

By
Rachel Adelson

December 2005, Vol 36, No. 11

Print version: page 16

Slim postpartum pickings for young birds may stunt their brain growth and impede their ability to later remember where they store food. In fact, early deprivation may send adult birds into a downward spiral and thwart their survival, according to new research by Vladimir Pravosudov, PhD, of the University of Nevada, Reno, and Pierre Lavenex, PhD, and Alicja Omanska, PhD, of the University of California, Davis.

They studied the impact of early malnutrition on the western scrub-jay, a long-tailed, blue-feathered songbird. They underfed scrub-jay chicks. Then a year later, when these scrawny chicks grew up, they were worse off as adults than birds who ate better when young-even though the experimental group had caught up by then in weight. The experimental birds had smaller hippocampi with fewer neurons than the control birds and performed worse on spatial-memory tasks that required them to recover seeds they had cached away.

Writing in the October issue of APA's Behavioral Neuroscience (Vol. 119, No. 1), the researchers concluded that the early nutritional deficits have long-term consequences that "are likely to have a strong impact on the animal's future fitness." Because mammalian brains also have hippocampi, the findings have "important implications for humans, particularly with regard to the effects of nutrition on the development of the brain and cognition," says Nicky Clayton, PhD, a professor of comparative cognition at Cambridge University who studies nutrition and cognition.

Although low birth weight across animal species and in humans has been associated with subsequent cognitive problems, this study offers new insight into nutrition after birth or hatching, when many species continue to "grow" their nervous systems. Previous studies have demonstrated that early food deprivation can affect brain and cognitive development in birds and mammals, says Clayton, but this study extends those findings by contrasting a spatial with a nonspatial task in analyzing hippocampal volumes and neurons.

These animal findings square disturbingly with the human condition: The U.N. Food and Agricultural Organization's 2004 hunger survey links stunted growth with increased illness and death, lower cognitive ability and school attendance in childhood, and lower productivity and lifetime earnings in adulthood. To give a sense of the problem's magnitude, the U.N. group counts the world's hungry at 852 million between 2000 and 2002, with nearly a third of the children in developing countries chronically undernourished.

Birds of a feather

To examine the effects of such undernourishment, Pravosudov and his colleagues randomly assigned 24 week-old western scrub-jays to experimental or control groups. Using syringes, they hand-fed control chicks until they were sated, but gave experimental chicks just two-thirds of the amount given to controls. The chicks were hand-fed until they all started eating on their own, at about one month old.

At that point, the researchers gave the jays all the food they wanted; the birds immediately started caching peanuts, bird pellets, waxworms and mealworms. The researchers let the birds grow for six months or so, during which time the deprived chicks caught up to the control birds in body mass, though not quite in stature.

Pravosudov and his colleagues then tested the birds one by one in a room where, from a high perch, the birds could survey 38 evenly distributed two-inch holes-potential cache sites filled with sand for burying food.

To test spatial memory, the experimenters deprived each bird of food for 24 hours, then gave it 30 waxworms and 20 food pellets. For 40 minutes, the birds ate and stowed their leftovers. The researchers then inventoried cache sites. For the next-day recovery phase, researchers covered the caches with fresh sand to deprive birds of local information, then tested hungry birds for 20 minutes as each jay searched for the food it stored the day before. Every time a bird probed a cache site, it was counted as a "search."

Several months later, the researchers also tested the control and experimental birds' associative learning in spatial tasks, rewarding the jays for looking for food in previously rewarded (with mealworms) locations. To see if color aided search, they added red and blue tape to the target location when the birds were over nine months old. They also associated food directly with one of five available colors.

Nutritionally deprived birds were as active as control birds, but had to inspect significantly more sites-about twice as many-to find their caches after either one or 10 days. On the associative-learning task, the deprived birds again searched significantly more sites to find the one that had been associated with food. Color didn't matter, indicating that early malnutrition hurt spatial, but not color, memory.

What's more, once the developmental window closed, eating enough during maturity didn't make up for early malnutrition. Given that a bird must remember where it buried its food, insufficient parental feeding early in life could mean baby, once grown, may face more of a life-or-death struggle in the wild.

Food for thought

Pravosudov speculates that if it takes a lot of energy to build the brain, malnutrition could result in underbuilding-roughly analogous to a builder running out of two-by-fours and skimping on rooms, depending what's left to build. And in the "house" of the human brain, notes Pravosudov, memory is "the last to form during development and the first to go during aging."

Still, given the importance of spatial memory to food-caching birds, why can't the body protect the hippocampus? Stephen Nowicki, PhD, the Dean of Natural Sciences at Duke University, and Wiliam Searcy, PhD, a biologist with the University of Miami, Coral Gables, speculate in the same issue of Behavioral Neuroscience that natural selection sets investment priorities among the various developing parts of the nervous system.

Suffering environmental stress such as extreme cold, parasites or malnutrition, an organism performs "triage" on developing systems, sacrificing some to protect others. In investment terms, the brain is rebalancing its portfolio-and Nowicki and Searcy suspect that neural systems, just like anatomical and physiological systems, set investment priorities. Thus, postnatal stress slams the hippocampus and the cerebellum, also a fast early-life grower.

But then nature isn't always kind-or fair. Write Nowicki and Searcy, "The brain is a particularly expensive organ to build and it is unlikely to be spared entirely if poor conditions prevail during development." They hope that future study will illuminate how the brain makes trade-offs when different species adapt to deprivation.